a
b
c
Need to think about this question 2 ways
1. within neurons –
2. between neurons-
Neuron receiving info
Information traveling
down neuron

within neurons – electrically

between neurons – chemically
◦ Synapse – space between neurons


developed Golgi
Stain
first determined
space between
neurons
 “synapse”

the “resting” state

the “active” state
◦ neuron is firing
◦ action potential

the “refractory” state

giant squid axon

inside of the axon has a slightly negative
charge relative to outside the axon
◦ called the membrane potential
◦ usually around -70mV

inside of the axon has a slightly negative
charge relative to outside the axon
◦ called the membrane potential

why?
action potential or
spike

see depolarization (change from negative
inside neuron to more positive)
action potential or
spike

see depolarization (change from negative
inside neuron to more positive)
◦ “threshold” – if a great enough depolarization
occurs, an action potential will occur
◦ action potential – very quick – milliseconds
 Other terms – spike, firing, generating an AP
action potential or
spike

Hyperpolarization
 return to negative
 this is the refractory or recovery period
action potential or
spike

All axons and cells have a membrane
 thin lipid (fat) bilayer



The membranes have channels (to allow ions
in or out)
Ions – molecules with a charge
These channels can be open or shut


Ions flowing across the membrane causes the
changes in the potential
Ions are molecules that contain a positive or
negative charge
 anion – negative charge
 cation – positive charge




Na+
sodium
◦ HIGHER CONCENTRATION OUTSIDE THE AXON
Clchloride
◦ HIGHER CONCENTRATION OUTSIDE AXON
K+
potassium
◦ higher concentration inside the axon
A- anions -large (-) molecules with a negative
charge (stuck inside the axon)
INSIDE AXON
(intracellular)
OUTSIDE AXON (EXTRACELLULAR
FLUID)
Na+
Cl-
Na+
A-
A-
Cl-
ClA-
Cl-
Cl-
Na+
Cl-
Na+
Na+
Cl-
Na+
Na+
AA-
Na+
Na+
Na+
Na+
Cl-
Cl-
ClA-
Na+
Na+
ClClCl-
Cl-
Cl-
Na+ and Cl- are in higher concentration
in the extracellular fluid
Neuron at Rest
INSIDE AXON
OUTSIDE AXON (EXTRACELLULAR FLUID)
ClK+
A-
K+
K+
ClNa+
Cl-
A-
Na+
K+
Na+
A-
K+
Na+
K+
Cl-
Na+
A-
Cl-
Na+
K+
K+ and negative anions are in higher concentration
in the intracellular or inside the axon
Neuron at Rest

concentration gradient –
◦ ions diffuse from higher concentration to lower
concentration
example of concentration forces
What would each ion do if the ion channel opened
based on the concentration gradient?
Na+
K+
Cl-

concentration gradient –
◦ ions diffuse from higher concentration to lower
concentration

electrical gradient ◦ opposite charges attract so ions are attracted to an
environment that has a charge that is opposite of
the charge they carry!
example of electrostatic forces
What would each ion do if the ion channel opened
based on electrostatic forces ?
Na+
K+
Cl-
INSIDE AXON
(intracellular)
A-
A-
Cl-
OUTSIDE AXON (EXTRACELLULAR
FLUID)
Na+
Cl-
A-
Cl-
ClCl-
Na+
Na+
Na+
Na+
Cl-
Na+
Na+
AA-
Cl-
Na+
Na+
Na+
Na+
Cl-
Cl-
ClA-
Na+
Na+
ClClCl-
Cl-
Cl-
Na+ and Cl- are in higher concentration
in the extracellular fluid
Axon depolarizing

opening of Na+ channels and influx of Na+
ions

lidocaine,
novocaine, cocaine

TTX – tetrototoxin

Sagitoxin◦ red tides
Concentration
Gradient
Electrical
Gradient
Na+
K+
Cl-
after the AP (+ intracellular)
INSIDE AXON
OUTSIDE AXON (EXTRACELLULAR FLUID)
ClK+
K+
K+
A-
ClNa+
Cl-
A-
Na+
K+
Na+
A-
K+
Na+
K+
Cl-
Na+
A-
Cl-
Na+
K+
K+ and negative anions are in higher concentration
in the intracellular or inside the axon
Neuron at Rest
Sodium-potassium pump – active force
that exchanges 3 Na+ inside for 2 K+
outside
INSIDE AXON
OUTSIDE AXON (EXTRACELLULAR FLUID)
Cl-
Na+
K+
K+
A-
ClNa+
Na+
Cl-
A-
Na+
K+
Na+
Na+
K+
Na+
Cl-
Na+
A-
K+
Na+
A-
Na+
Cl-
Na+
K+
K+
K+ and negative anions are in higher concentration
in the intracellular or inside the axon
After the action potential

myelin sheath (80% fat and 20% protein)
◦ produced by glia
http://www.blackwellpublishing.com/matthews/channel.html
nodes of ranvier

myelin sheath (80% fat and 20% protein)
◦ produced by glia
◦ nodes of ranvier
nodes of ranvier

myelin sheath (80% fat and 20% protein)
◦ produced by glia
◦ nodes of ranvier
◦ saltatory conduction (200 ft/sec)
http://www.blackwellpublishing.com/matthews/actionp.html

speed, efficiency of neurotransmission

speed, efficiency of neurotransmission

disease: Multiple Sclerosis
 progressive, autoimmune disease
 onset ~ 20 years of age
 early symptoms: motor symptoms, such as weakness,
leg dragging, stiffness, a tendency to drop things, a
feeling of heaviness, clumsiness,
What about communication between
neurons?